Demands for cellular downlink data are rapidly increasing as consumers use greater numbers of data intensive applications on their wireless data devices. This trend is encouraging wireless carriers and wireless service providers to explore new ways of increasing downlink data rates. One known method for increasing downlink data rates employs receive carrier aggregation. Receive carrier aggregation allows a wireless device to simultaneously receive data using multiple downlink frequency bands to improve throughput while simultaneously transmitting on another band. Receive carrier aggregation may be either contiguous or non-contiguous. In the case of non-contiguous carrier aggregation, receive carrier aggregation may be applied either intra-band or inter-band. The present disclosure relates to non-contiguous inter-band operation where a second receive band is located at a third harmonic (H3) of a transmit frequency.
In non-contiguous inter-band operation where one of the receive bands is located at the H3 of the transmit frequency, the harmonics generated in a power amplifier (PA) and front end (FE) switches are not attenuated sufficiently enough to prevent receiver desensitization. Related art methods for reducing receiver desensitization due to harmonics include improving a lower band duplex filter attenuation of the third harmonic of the TX frequency, improving the diplexer low band/high band (LB/HB) isolation, and adding continuously active (i.e., static) notch filters into the TX path, and the implementation of dual feed antennas with inherent LB/HB isolation.
However, these related art methods such as adding static notch filters into the TX path may not be directly applicable to antenna tuning components. For example, an antenna can be tuned by changing the impedance of the ground connection of the antenna. An RF switch is commonly used to switch this impedance. The location of the RF switch relative to the antenna may make it difficult or impossible to implement diplexers, lowpass filters, notch filters, etc. A better approach is to eliminate the need for filtering by reducing the amount of H3 produced by switch branches making up FE switches. Therefore, a need remains to reduce the H3 in components making up the FE switches in order to attenuate the generated H3.